Larson began his career in the entertainment industry in 1956 as a member of the vocal group The Four Preps, with whom he appeared in one of the Gidget films. The Four Preps ultimately produced three gold records for Capitol, all of which Larson wrote and/or composed: "26 Miles (Santa Catalina)", "Big Man", and "Down By The Station." A later member of the Four Preps, David Somerville, and a session singer he knew, Gail Jensen, later collaborated with Larson to write and compose "The Unknown Stuntman", the theme from The Fall Guy, whose lead cast member, actor Lee Majors, performed the selection over the opening titles.

After working for Quinn Martin Sr. on productions including The Fugitive, Larson signed a production deal with Universal Studios. His first hit series was Alias Smith and Jones, a Western which described the activities of Hannibal Heyes and "Kid Curry", concentrating on their efforts to go straight. (George Roy Hill's film, scripted by William Goldman, about Butch Cassidy and the "Sundance Kid" is commonly believed to have been the inspiration for the series.)

Larson was involved in the development for television of The Six Million Dollar Man, based on Martin Caidin's novel Cyborg, into the successful series that starred Lee Majors in the title role, and was one of the program's early executive producers.

Larson later secured a then-unprecedented $1 million per episode budget for Battlestar Galactica. Originally, the series was intended to be called Adama's Ark, and the show incorporated many themes from Mormon theology, such as marriage for "time and eternity" and a "council of twelve." Larson, a member of The Church of Jesus Christ of Latter-day Saints in real life, had been working on the concept since 1968, and Gene L. Coon had been providing guidance and mentoring to him through the writing of its earliest incarnations. Larson is credited with coining the word "battlestar," a contraction of the phrase "line-of-battle starship", after being convinced to rename Adama's Ark to include the word "star" in the title in some way. He is also credited with creating the faux curse word "frak."

Even with its generous budget, the series often recycled effects shots; it was canceled after one season. The pilot episode of Galactica, entitled "Saga of a Star World" in the program continuity, was refashioned as a theatrical release in North America and Europe, and in some European markets it was the top grossing film of 1979. After the series was canceled, Larson went on to create a relatively low-budget sequel to the series entitled Galactica 1980 which was set many years later when the Galactica had reached Earth. This series was less successful than the original and was canceled after 10 episodes.

Larson re-used some of the sets, props, costumes, and effects work from Galactica to create the light-hearted sci-fi series Buck Rogers in the 25th Century (1979). The show starred Gil Gerard, Erin Gray, Mel Blanc (voice of Twiki), Pamela Hensley and the great English actor Wilfrid Hyde-White. The feature-length pilot episode was released as a theatrical film in March 1979 and grossed $21 million at the North American box office.

In the 1980s, Larson garnered further success as one of the creators of Magnum, P.I., which ran from 1980-88. Additionally, Larson created The Fall Guy, starring Lee Majors, which ran from 1981-86. Larson's next prominent series was Knight Rider, which starred David Hasselhoff and featured science-fiction elements with a light-hearted action-adventure scenario and limited violence. These basic elements characterized much of Larson's output throughout the 1980s with Automan, Manimal, and The Highwayman, though all of these series were unsuccessful and none lasted more than a single season. Larson's popularity declined, though he made a brief comeback in the 1990s with an adaptation of the Ultraverse comic Night Man, which lasted two seasons.

In February 2009, internet media sources reported that Larson was in talks with Universal Pictures to bring Battlestar Galactica to the big screen, though any potential feature film would not be based on the recent Sci Fi Channel series remake, but would possibly be based on the original series which starred Richard Hatch, Dirk Benedict and the late Lorne Greene. On August 14, 2009, it was reported that the new film was "a complete re-imagination" and Bryan Singer had signed to direct and produce the new film with Larson as producer.

Honors

Larson has a star on the Hollywood Walk of Fame for his contributions to the television industry.

• It Takes a Thief (1968) (TV series) (associate producer) (producer)
• McCloud (1970) (TV series) (executive producer) (producer)
• The Virginian (1962) (TV series) (executive producer) (1970—1971)
• Alias Smith and Jones (1971) (TV series) (producer)
• The Six Million Dollar Man: Wine, Women and War (1973) (TV movie) (executive producer)
• The Six Million Dollar Man: The Solid Gold Kidnapping (1973) (TV movie) (executive producer)
• Sin, American Style (1974) (TV) (executive producer)
• Get Christie Love! (1974) TV Series (executive producer)
• Switch (1975) (TV series) (executive producer)
• Quincy, M.E. (1976) (TV series) (executive producer)
• Las Vegas Undercover (1977) (TV) (producer)
• The Hardy Boys Mysteries (1977) TV Series (executive producer)
• This was based on the Stratemeyer Syndicate novels credited to "Franklin W. Dixon."
• Hardy Boys/Nancy Drew Mysteries (1977) TV Series (executive producer)
• This was a television development of Stratemeyer Syndicate novels credited to two fictitious authors, "Franklin W. Dixon" (as noted above) and "Carolyn Keene."
• Battlestar Galactica (1977-1978)
• The Islander (1978) (TV movie) (producer)
• Sword Of Justice (1978) TV Series (executive producer) (producer)
• Evening in Byzantium (1978) (TV) (executive producer)
• A Double Life (1978) (TV) (executive producer)
• This is the pilot installment of Sword of Justice, which starred Dack Rambo in the lead. Larry Hagman was the villain in this story, which predated his and Rambo's characters in Dallas also being antagonists.
• B. J. and the Bear (1979)
• Buck Rogers in the 25th Century (1979)
• The Misadventures of Sheriff Lobo (1979) TV Series (producer)
• The Murder That Wouldn't Die (1980) (TV) (executive producer, uncredited)
• Galactica 1980 (1980)
• Magnum, P.I. (1980) (also joint writer, with Donald P. Bellisario, of pilot)
• Donald P. Bellisario took over as primary executive producer after the pilot installment, "Don't Eat The Snow In Hawai'i."
• Nightside (1980) (TV movie) (executive producer)
• The Fall Guy (1981) TV Series (executive producer)
• Fitz and Bones (1981) TV Series (producer)
• This crime drama starred the Smothers Brothers, Thomas Smothers and his younger brother Richard "Dick" Smothers Sr., but the characters they acted out were not brothers.
• Knight Rider (1982)
• Predating Baywatch by several years, this action-adventure program, which starred David Hasselhoff, became the most successful of Larson's productions to date.
• Terror at Alcatraz (1982) (TV) (executive producer)
• Rooster (1982) (TV movie) (executive producer)
• Manimal (1983) TV Series (producer)
• Automan (1983) TV Series (executive producer)
• Cover Up (1984) TV Series (executive producer)
• Model-turned-actor Jon-Erik Hexum died as a result of playing "Russian roulette" with one of the prop pistols, and Australian actor Antony Hamilton gained his "big break" in the United States taking over for Hexum. But without Hexum, the program failed and was canceled without lasting a full season.
• In Like Flynn (1985) (TV) (executive producer)
• The Highwayman (1988) (TV series) (executive producer)
• The Road Raiders (1989) (TV) (executive producer)
• Chameleons (1989) (TV movie) (executive producer)
• P.S.I. Luv U (1991) TV Series (executive producer)
• One West Waikiki (1994) TV Series (executive producer)
• Night Man (1997—1999)
• Team Knight Rider (1997) TV Series (executive producer)
• The Darwin Conspiracy (1999) (TV) (executive producer)
• Millennium Man (1999) (TV) (executive producer)
• Battlestar Galactica (2003) (mini) TV Series ("consulting producer")*
• Battlestar Galactica (2004) TV series ("consulting producer")*
• Caprica (2010) TV series ("consulting producer")*

(* Although credited as "Consulting Producer" on the 2003 remake of Battlestar Galactica and its spin-off Caprica, Larson actually had no direct involvement with either series.)